Process for electroplating molybdenum and its alloys



Patented Mar. 7, 1950 PROCESS FOR ELECTROPLATINGr-.MQLYB- DENUM ANDITSALLOYS Leonard F. Yntema, Webster Groves, and Mary Joecile, Ksycki. St.Louis, Mo., assignors to president and board of trustees of St. LouisUniversity, St. Louis, M0.

N Drawing. Application August 31, 1942, Serial No. 456,820

- solai s. ((1204-43) A The invention relates to the electrodeDQSifionof molybdenum.

We have discovered that molybdenum maybe efficiently.electrodepositedfrom aqueous electrolytes containingmolybdic acid, its anhydride oritssalts. in the presence of aliphatic acids and highconcentrations ofsalts of aliphatic acids.

Among .the additional salts which may advantageouslybeused in ourprocess are the sodium, potassium or,.ammonium formate, acetate, andpropionate or. combinations of the same. It is of advantage to employsuch concentrations of these saltsthat the mol ratio of added anion towater is from 1 to 2 up to 1 to 4, preferably between 1 1302.2 and 1 to3.

The work on which the electrodeposition of molybdenum is desired isplaced in the electrolyte vto form the cathode and the anode. is aconducting material which will notbe attacked by the reaction productsat the anode, such as platinum or carbon. A cathode of copper, iron, ornickel has been found to be satisfactory.

The electrolytic bath is preferably maintained slightly acid. theoptimum conditions being a pH between 5.5 to 6.8 as measured with a lasselectrode. Under some conditions however the pH maybe varied from thisrange and, in particular, a potassium-ammonium propionate bath willgivegood deposits at a pH of 7.4.

The current density may be varied quite widely but the optimumconditions arev between 0.1 to

0.8 ampere per square centimeter of cathode surljace. 1he temperature ofthe bath is. preferablvv maintained between 30 C. and 50? C.

,Wi h ur processes above des b we. ave been able to. obtain. smooth,bright, adherent deposits of molybdenum in two minutes. The depositedmetal is resistant to acids such as 0 1d hydrochloric and sulfuric andis resistant to stron uallialies but is soluble in nitricacid.

Our process is adapted for the electrcplating of articles. to renderthem corrosionresistant as well as to obtain a bright decorative effect.It is usefulfor preparing: molybdenum sheet byobtaining a thi k depositi -th m ta on ui abl ca a d'subsequ n i solv n o f. e cathode ea ins-thel e m n. she .io

Our process isadapted for theelectrodeposition of molybdenum alloys ormixtures with other metals Iron may be codeposited with molybdenum byadding to the bath a solution of a ferrous salt, such as ferrous ,ilfate (F8804). Cobalt m e, cod p sit d wi h ely d m, y adding tothe th asolution of acobalt salt, such as coj iidsel. be Qdee s t 2 withmolybdenum by adding to the bath asolutime of. n kel-sa s hasnicke1...su1. .(N'iSOi).

The. anions of. .thealiphaticacids, ,,such,, as formate, acetate, andpropionate. which are pres:- ent in. high concentration increase thesolubility f e he t mo1ybden compounds in the acid olutionsand. withthe, acid, increa hQSQ ubility of reduction products of -the hexavalento bd um compo nds .forme ur the P cessor electrolysis therebypreventingthe precipitation. Oi, molybdenum hydroxide orf of basic salts.

One of the chief advantages of our process is that the molybdenum..Gp,n,1pounds used are the most readily available compounds of theelement. Molybdic anhydride, M003; and ammonium paramolybdate,(NH4)5M07O24.4H2O are both-,commercially available and are bothoperative in our process.

To illustrate our invention, the following-1e):- amples are given:

Example I An electrolyte is made up of the following vcomposition: 5 g.molybdicanhydride so g. KOH 55 co. NH'iQ 1 8% N s 75 cc. HCOzH' (8'7 cc,H V Preferablythe bath is subjected. to apreli ninary electrolysis at acurrent density of 0.53ampere per square centimeter until the bathbecomes red in color. The optimum conditions for ob- .t ni amowbde m .frm th s: ba h are. PH,

to 5.9; current density 0.5 ampere per squarecentimeter; temperature C.to C. Bright metallic deposits of molybdenum are. obtained in -fiveminutes. The weight of anaveragez-deposit is 0.5 mg. on an area of 8square centimeters of cathode surface. The current densitynan cforbright metal plating from this bath.is .,0.35 to 0.6 ampere per squarecentimeter.

. mlllc II nnelectrolyte made up of the, followingcomposition:

5 g. molybdic anhydride g NH4C2H302 50 g-rKt'JzHsOa l0 col-ICnI-lcOc-(glacial) cc. -;H2Q

No preliminary electrolysisis---needed. '-1 he optimum conditions forobtaining deposition of molybdenum from this bath are pH 5.7 to 6.0;current density 0.5 ampere per square centimeter; temperature 30 C. to40 C. Bright metallic deposits of molybdenum are obtained in twominutes. The weight of an average deposit is 1.0 mg. on 8 squarecentimeters of cathode surface. The current density range for brightmetal plating is from 0.2 to 0.6 ampere per square centimeter.

Example III An electrolyte is made up of the following composition:

g. molybdic anhydride 74 cc. prooionic acid (HC3H5O2) 32 gm. (NH4) zCOs19 gm. X011 28 cc. H2O

Example IV An electrolyte is made up of the following com- "position:

5 g. mol bdic anhydride 60 g. KOH

55 cc. N -T4OH (28% NH3) '75 cc. HCOzH (87%) 15 cc. H20

30 cc. FeSO4 (0.1 M)

The optimum conditions for the codeposition of molybdenum and iron fromthis bath are a current density of 0.2 ampere per square centimeter:temperature 30 C. to 40 C. Bright metallic plates are obtained in twominutes. The current density range for bright metal plating from thisbath is 0.15 to 0.5 ampere per square centimeter.

Example V An electrolyte is made up of the following composition:

5 g. molybdic anhydride 50 g. NH4C2H302 cc. HCaHsOz (glacial) 65 cc. H20

3 cc. NiSO4 (0.1 M)

The optimum conditions for obtaining codeposition of molybdenum andnickel from this bath are current density 0.25 ampere per squarecentimeter; temperature 30 C. to 40 C. Bright metallic plates areobtained in one minute. The weight of an average deposit is 1 mg. on 16square centimeters of cathode surface. The current density range forbright metal plating from this bath is 0.07 to 1.0 ampere per squareCentimeter.

Example VI An electrolyte is made up of the following composition: 5 g.molybdic anhydride 50 g. NH4C2H3O2 50 g. KC2H3O2 10 cc. HC2H302(glacial) 65 cc. H20 1 cc. 005304 (0.1 M)

The optimum conditions for the codeposition of molybdenum and cobaltfrom this bath are current density 0.25 ampere per square centimeter;temperature 30 C. to 50 C. Bright metallic plates are obtained in oneminute. The weight of an average deposit is 0.5 mg. on 16 squarecentimeters of cathode surface. The current density range for brightmetal plating from this bath is 0.09 to 0.8 ampere per squarecentimeter.

The above examples are given by way of illustration only.

What we claim as our invention is:

1. The process of plating metallic molybdenum which comprises passing acurrent between an anode and the work to be plated as a cathode in anelectrolyte comprising an aqueous solution or a compound of the classconsisting of molybdic acid, its anhydride and its salts and a highconcentration of an anion of an aliphatic acid of the class consistingof formate, acetate and propionate, the ratio of said anion to waterbeing between 1 to 2 and 1 to 4 and the pH being between 5.5 and 6.8.

2. The process of plating metallic molybdenum which comprises passing acurrent between an anode and the work to be plated as a cathode in anelectrolyte comprising an aqueous solution of a compound of the classconsisting of molybdic acid, its anhydride and its salts and a high concentration of an anion of acetic acid, the ratio of said anion to waterbeing ofthe order of 1 to 2% and the pH being between 5.5 and 6.8.

3. An electrolyte for the electrodeposition of metallic molybdenumcomprising an aqueous solution of a compound of the class consisting ofmolybdic acid, its anhydride and its salts and a high concentration ofan anion of an aliphatic acid of the class consisting of formate,acetate and propionate, the ratioof said anion to water being between 1to 2 and 1 to 4 and the pH being between 5.5 and 6.8.

4. An electrolyte for the electrodeposition of metallic molybdenumcomprising an aqueous solution of a compound of the class consisting ofmolybdic acid, its anhydride and its salts and a high concentration ofan anion of an aliphatic acid of the class consisting of formate,acetate and propionate, the ratio of said anion to water being between 1to 2.2 and 1 to 3 and the pH being between 5.5 and 6.8.

5. An electrolyte for the electrodeposition of metallic molybdenumalloys comprising an aqueous solution of a compound of the classconsisting of molybdic acid, its anhydride and its salts, a highconcentration of an anion of an aliphatic acid of the class consistingof formate, acetate and propionate and a soluble salt of a metal of theclass consisting of iron, nickel and cobalt the ratio of said anion towater being between 1 to 2 and 1 to 4 and the pH being between 5.5 and6.8.

6. The process of electroplating metallicmolybdenum which comprisespassing a current between an anode and the.;work to be plated asf'acathode in an electrolyte comprising an aqueous solution of a molybdatecompound, an aliphatic acid of the class consisting of formic, acetic,and propionic acids and an alkali salt of an aliphatic acid of the classconsisting of formate, acetate and propionate, in which the ratio of theanion of said aliphatic acid and salt of said aliphatic acid to water isbetween 1 to 2 and 1 to 4, the pH being between 5.5 and 6.8, thetemperature being between 30 and 50 C. and maintaining the currentdensity between 0.07 and 1.0 ampere per square centimeter.

7. The process according to claim 6 in which the ratio of the anion ofsaid aliphatic acid and salt of said aliphatic acid to water ismaintained between 1 to 2.2 and 1 to 3.

8. The process according to claim 1 in which the anode is a conductingmaterial of the class consisting of platinum and carbon.

9. The process of electroplating metallic molybdenum alloys whichcomprises passing a current between an anode and the work to be platedas a cathode in an electrolyte comprising an aqueous solution of amolybdate compound, an aliphatic acid of the class consisting of formic,acetic, and

propionic acids and an alkali salt of an aliphatic acid of the classconsisting of formate, acetate and propionate, and a soluble salt of ametal to be codeposited with molybdenum of the class consisting of iron,nickel, and cobalt, in which the ratio of the anion of said aliphaticacid and salt of said aliphatic acid to water is between 1 to 2 and 1 to4, the pH being between 5.5 and 6.8, the temperature being between andC. and maintaining the current density between 0.07 and 1.0 ampere persquare centimeter.

LEONARD F. YNTEMA.

MARY JOECILE KSYCKI.

REFERENCES CITED The following references are of record in the file ofthis patent:

Quantitative Analysis by Electrolysis," by Classen and Hall, publishedin 1913 by John Wiley & Sons, Inc., page 146.

Transactions of the Electrochemical Society," vol. (1936) pages 423,424.

1. THE PROCESS OF PLATING METALLIC MOLYBDENUM WHICH COMPRISES PASSING ACURRENT BETWEEN AN ANODE AND THE WORK TO BE PLATED AS A CATHODE IN ANELECTROLYTE COMPRISING AN AQUEOUS SOLUTION OF A COMPOUND OF THE CLASSCONSISTING OF MOLYBDIC ACID, ITS ANHYDRIDE AND ITS SALTS AND A HIGHCONCENTRATION OF AN ANION OF AN ALIPHATIC ACID OF THE CLASS CONSISTINGOF FORMATE, ACETATE AND PROPIONATE, THE RATIO OF SAID ANION TO WATERBEING BETWEEN 1 TO 2 AND 1 TO 4 AND THE PH BEING BETWEEN 5.5 AND 6.8.